The common intestinal parasite known as pinworm or threadworm is affecting some Sisters residents. A pharmacist at Bi-Mart said Friday that the store’s inventory of pinworm medicine had sold out.

Symptoms include itching of the anal or vaginal area; insomnia, irritability, and restlessness; and intermittent abdominal pain and nausea, according to the Mayo Clinic. Some infected people have no symptoms at all.

The culprit is a white or yellowish roundworm called Enterobius vermicularis that’s about as long as a staple. Pinworms dwell in the colon and rectum of humans, infecting 20 percent or more of the population. They are most common among children and people who live in institutions — along with their caregivers and household members.

While the infected person sleeps, female pinworms leave the intestine through the anus and lay eggs on the surrounding skin, causing itching and discomfort.

While pinworms are not generally considered a serious health problem, there is a slight risk of more harmful infection such as vaginitis or endometritis, according to the Mayo Clinic.

Local nurse Beth Hummel, R.N., said she would worry about pinworms “getting up into the fallopian tubes, because of the damage they can do, and how uncomfortable for that little girl — or a grown girl, anyone with the plumbing.”

In rare cases, pinworms may also cause urinary tract infection (UTI).

The eggs live up to three weeks outside the body — on skin, bedding, toilets, and toys. People usually become infected via the “oral-fecal route,” where the sticky eggs are transferred via skin or fingernails to food, linens, or other surfaces.

Unknown to many medical practitioners, the Centers for Disease Control and Prevention and Mayo Clinic now report that pinworm eggs can become airborne. Inhalation may cause infection.

“I would love to see how often that actually happens,” said Andy Mohler, a pharmacist at BiMart.

“Don’t shake your sheets out,” said Hummel. “Oh, mercy.”

Emily Livengood, N.D., of Baker Family Naturopathic advised that patients receive a definitive positive diagnosis of pinworm before attempting treatment.

Diagnosis involves obtaining samples from the rectal area. A doctor may diagnose them by sight. Patients may have to collect a sample themselves using a strip of tape and send to a laboratory.

Albendazole or Mebendazole were formerly the go-to prescription drugs for treating pinworms. Some doctors still prescribe them, not realizing that the drugs have skyrocketed in cost.

A recent prescription cost $800 at a Central Oregon pharmacy.

The corporations Amedra Pharmaceuticals and its acquirer Impax Laboratories created a monopoly on prescription pinworm medication in the U.S., according to Consumer Reports. They launched a $400 chewable pill and took the inexpensive version off the market.

There is an over-the-counter alternative. Reese’s Pinworm Medicine (Pyrantel Pamoate Suspension) costs $20-25.

Andy Mohler, a pharmacist at Bi-Mart in Sisters, said it is now back in stock.

“It seems to cycle,” Mohler said of pinworm medicine purchases at the store. “We get a rush for a while, then it disappears. We get some on the shelf and they sit for a very long time. Then there’s a rush, then it disappears again.”

Mohler said he didn’t know if “everyone overreacts” to sudden outbreaks, “or if they’re actually being tested and showing positive. It can become a panic situation with families.”

Killing the worms themselves is a small part of treating pinworm. The tenacious eggs, viable for three weeks, are unwittingly spread around by humans.

Avoiding reinfection takes weeks of intensive cleaning and preventive measures (see sidebar, “Preventing Pinworm Infection,” page 17). Many patients follow up with a second dose two weeks later, followed by three more weeks of intensive cleaning and hygiene.